1. Field of the Invention
The present invention relates to an image forming apparatus and a storage medium storing a diagnostic program used therewith, and more particularly, to an inkjet image forming apparatus that employs an ink container to supply ink liquid to a printhead for ejecting ink droplets, and a storage medium storing a computer-executable diagnostic program for use in such an image forming apparatus.
2. Discussion of the Background
Inkjet printing is widely used in various image forming apparatuses, such as printers, facsimiles, photocopiers, plotters, and multifunctional machines having image forming capabilities, in which an ink image is formed by a movable printhead ejecting droplets of ink through multiple nozzles onto a recording medium or recording sheet conveyed below the printhead.
In common inkjet printers, the printhead is integrated with a subtank or ink container defining an ink chamber, which serves to hold ink received from a replaceable ink cartridge mounted on the printer body and immediately supply ink as needed by the printhead during printing. Typically, such a subtank is equipped with a pressure generator that generates a negative pressure or back pressure lower than the atmospheric pressure within the ink chamber and its associated printhead. This negative pressure prevents ink from leaking or dripping by gravity from the printhead, thereby maintaining proper ink ejection and good imaging performance of the inkjet printer.
For example, one conventional inkjet printer employs an open-sided subtank having an elastic film to cover its open side to define a sealed ink chamber therein, and a spring to bias the elastic film outward from within the ink chamber. To depressurize the ink chamber, the printer fills the ink chamber with ink, hermetically sealing the ink chamber by closing its opening, and discharges a certain amount of ink through the printhead with the biasing spring maintaining the original volume of the ink chamber.
It is known that the negative pressure generated in an ink chamber of a subtank tends to dissipate as air leaks into the subtank from the atmosphere over time. Upon detecting air leak and pressure loss in the ink chamber, the conventional printer automatically performs the depressurizing process so as to maintain a good level of negative pressure in the subtank and good ink ejection by the printhead.
However, one drawback of such a conventional method is that handling air leakage by pressure generation is ineffective where the air leak results from a mechanical defect in the subtank, such as even a small amount of foreign matter lodged in a ventilation valve to unseal the ink chamber, a loose connection between a supply tube and the ink chamber, or cracks or flaws in worn parts forming the ink chamber, etc., which allows air to continually leak into the ink chamber and immediately dissipate a generated negative pressure. In such cases, automatically repeating pressure generation only increases amounts of wasted ink and time, resulting in significant inconvenience to the user of the conventional image forming apparatus.